Method of making turbine blades



' 1966 J. R. BIRD ETAL 3,

METHOD OF MAKING TURBINE BLADES Filed April 10. 1961 United States Patent 3,228,095 METHOD OF MAKING TURBINE BLADES Jack Raymond Bird, Chellaston, Douglas Wilson Hall, Mickleover, and David Anthony Denton, Chellaston, England, assignors to Rolls-Royce Limited, Derby, England, a company of Great Britain Filed Apr. 10, 1961, Ser. No. 101,806 Claims priority, application Great Britain, Apr. 13, 1960, 13,287/60 6 Claims. (Cl. 29156.8)

This invention concerns the production of the turbine rotor and stator blades of a gas turbine engine.

In the modern gas turbine engine the turbine rotor and stator blades are required to withstand very high temperatures and stresses for long periods of operation. In order to meet these requirements, the materials (e.g. nickel based alloys) used in the production of these blades have a high content of strengthening constituents and are therefore difiicult to work. Accordingly, as the gas turbine engine becomes more and more highly developed it becomes increasingly difficult to form its turbine blades. The object of the present invention is therefore to provide a method by means of which such blades may be satisfactorily made.

According to the present invention there is provided a method of making a turbine rotor or stator blade of a gas turbine engine comprising casting a mass of the material from which the blade is to be made, and employing substantially the whole of the cast mass in the production of a single turbine rotor or stator blade, the blade being formed from the cast mass by a process which involves a forging operation.

In its preferred form the invention comprises a method of making a turbine motor or stator blade of a gas turbine engine from an alloy having the following percentage composition by weight:

Percent Cr -30 Co 0-30 Mo 5-30 W 0-20 Ti 0.5-7.0 Al 20-17 B 0.003-03 Zr 0.00l-1.0 C 0.01-0.5 Ca 0-0.1 him OO.4 Si 0-0.4 Fe O1.0 Be 00.5 Ta 0-5 Nb 0-5 Hf 0-10 Rare Earths 0-0.2 S 0-0.005 P 0-0.008 V 0-3 N 0-0.2 Mg 0-0.15 Combined O 0-0.2 Cu 0-0.5 Pb 0-0.005

the combined titanium and aluminum content of the alloy being at least 6.5% and the balance of the alloy being nickel and impurities, there being at least 35% of nickel if cobalt is present or at least 45% of nickel if cobalt is not present, said method comprising casting a mass of the alloy, and employing substantially the whole of the cast mass in the production of a single turbine rotor or stator blade, the blade being formed from the cast mass by a process which involves a forging operation.

We have found that the chief problem in forming blades of the above-mentioned alloy is to break down the coarse columnar crystal structure which the alloy has previously had in the as cast condition without exceeding the maximum shear strength of individual crystals and without forming microscopic flaws or very small cracks. We consider that the coarse crystal structure referred to above has previously been caused by casting the alloy into large ingots, since the central portion of these large ingots is very slow to cool from the liquid to the just solid state and this slow cooling permits the growth of large crystals. In the method of the present invention, however, the alloy is cast into very small masses since these masses are of a size such that only one turbine blade can be produced therefrom. Accordingly the cooling of such small masses is rapid with the result that they have relatively fine grains. Such small masses are then forged into turbine blades, faults present in the castings normally being made apparent as a result of the forging operation.

Although it is an essential feature of the present invention that each casting should be such that only one turbine blade can be formed therefrom it should be understood that the term casting, as used in this specification, is intended to cover the case where the casting is one of a number of interconnected castings produced from a corresponding number of moulds having a common runner.

Preferably the allow is cast in the form of a dumbellshaped blade blank (which is known as a use).

The surface of the cast alloy may be subjected to cold work prior to the said forging operation.

The forging operation may conveniently be performed in two stages with a short high temperature heat-treatment therebetween. This may have the effect of increasing the creep resistance of the resulting blade.

The invention is illustrated by the following Example, reference being made in the accompanying drawings, FIGURES 1-4 of which show side views and end views of a turbine blade at various stages of its manufacture.

Example An alloy having the following percentage composition by weight:

Percent Carbon 0.11 Chromium 14.80 Cobalt 10.20 Molybdenum 8.08 Aluminium 4.60 Titanium 4.42 Boron 0.005 Zirconium 0.002 Iron 0.30 Silicon 0.14 Manganese 0.10 Sulphur 0.002 Nickel Balance essentially was vacuum melted and was vacuum cast to form a use 10, that is to say a dumbell-shaped blade blank. The use 10 was inspected by X-ray methods and was given an homogenisation heat-treatment at 1200 C. for 2-24 hours.

The use was then machined to size to produce a blank 11 and was inspected for surface defects, after which it was subjected to a controlled amount of surface cold work by shot peening, reeling, or cold swaging.

The blank 11 was then given a first recrystallization treatment at 1150-1250 C. for 10 minutes and was quenched if necessary. After being vapour blasted, the blank 11 was nickel plated or glass coated so as to provide it with a surface lubricant and was then heated to 1200 C., after which it was press forged a controlled amount to a first deformation 12. It was then given a second recrystallization treatment at 1200" C., and was thereafter press. forged to a second deformation 13 which constituted its final shape. The blade was finally heattreated to give optimum qualities, e.g. by a solution heattreatment and by an ageing heat-treatment at one or two temperatures.

In the case of some alloys, it may be necessary, immediately prior to the final heat-treatment, to give the blade a further recrystallization treatment and to press forge it again.

Moreover, in the case of some alloys it is possible to omit the homogenization heat treatment, the machining to size, the surface cold work, the first recrystallization treatment, and by the vapour blast.

We claim:

1. A method of making a turbine blade of a gas turbine engine from an alloy having the following percentage composition by weight:

Percent Mn 0-0.4 Si 00.4

Be O-O.5 Ta 0-5 Nb -0-5 Hf 0-10 Rare Earths O-0.2

N 0-0.2 Mg 0-0.15 Combined O 0-0.2 Cu 0-0.5

the combined titanium and aluminium content of the alloy being at least 6.5% and the balance of the alloy being nickel and impurities, there being at least 35% of nickel if cobalt is present but at least 45% of nickel if cobalt is not present, said method comprising casting a mass of the alloy into the form of a dumbell-shaped blade blank, employing substantially the whole of the cast mass in the production of a single turbine blade, and forming the blade from the cast mass by a process which involves a hot forging operation.

2. A method as claimed in claim 1 in which the hot forging operation is performed in two stages with a high temperature heat-treatment at 1200' C. therebetween.

3. A method as claimed in claim 1 wherein the cast mass, before the forming operation, is given a homogenisation heat-treatment at 1200 C. for 2-24 hours and the subsequent hot forging operation is carried out in tWo stages with heat-treatment at 1200 C. therebetween.

4. A method of making a turbine blade of a gas turbine engine from an alloy having the following percentage composition by weight:

Percent Co 0-30 Mo 5-30 Al 2.0-17 B 0.003-0 3 Zr 0001-1 0 C 0.01-0.5

Ca 0-0.l

Mn O-O.4

Si O-O.4

Fe O-l.0

Be 0-0.5 Ta 0-5 Nb 0-5 Hf O-lO Rare Earths 0-0.2 S 0-0.00S

P 0-0.008 V O-3 N 0-0.2 Mg 00.1S Combined O O-0.2 Cu 0-O.5 Pb 0-0.005

the combined titanium and aluminium content of the alloy being at least 6.5% and the balance of the alloy being nickel and impurities, there being at least 35% of nickel if cobalt is present but at least 45% of nickel if cobalt is not present, said method comprising casting a mass of the alloy into the form of a dumbell-shaped blade blank, employing substantially the whole of the cast mass in the production of a single turbine blade, and forming the blade from the castmass by a processwhich involves subjecting the surface of the cast mass to cold work and thereafter subjecting the cast mass to a hot forging operation.

5. The method of claim 4 wherein the cast mass after coldworking is subjected to a recrystallization heat treatment before said hot forging operation and another recrystallization heat treatment after said hot forging operation.

6. The method of claim 4 wherein the hot forging operation comprises recrystallization heat treatment and press forging.

References Cited by the Examiner UNITED STATES PATENTS 2,447,897 8/1948 Clarke 29-1568 2,977,222 3/1961 Bieber -171 2,987,806- 6/1961 Pekarek 29-1568 3,047,381 7/1962 Hanink et al. 75-171 3,107,999 10/1-963- Gittus 75-171 3,110,587 11/1963 Gittus et'al. 75-171 FOREIGN PATENTS 548,777 11/ 1957 Canada.

CHARLIE T. MOON, Primary Examiner.

HYLAND BIGOT, WHITMORE A. WILTZ, Examiners J. D. HOBART, J. C. HOLMAN, Assistant Examiners. 

1. A METHOD OF MAKING A TURBINE BLADE OF A GAS TURBINE ENGINE FROM AN ALLOY HAVING THE FOLLOWING PERCENTAGE COMPOSITION BY WEIGHT: 